See IRC. We should disable this for diffs over a certain number of changes or something like that, since a ~50MB diff took more than 2 hours to process.
The file itself certainly does:
$ git show c84da7041b1199f051d041ca2cc86f3736e0898b:crowdin_data.pickle | sort | uniq -c | sort -n | tail 4612 Vlearn.math.cc-eighth-grade-math.exercises 4674 Vlearn.math.cc-sixth-grade-math.exercises 4863 Vlearn.math.calculus.exercises 4944 Vlearn.math.cc-seventh-grade-math.exercises 6181 Vlearn.math.early-math.exercises 7603 Vlearn.math.algebra.exercises 8504 Vlearn.math.trigonometry.exercises 54731 sg13 57871 g11 108380 g2
Not sure if there's something special I need to do to make reparse.php --message be slow again; P1148 shows its current (fast) output. The diffusion page for that commit says "Still Importing...".
If --message worked, do:
./scripts/repository/reparse.php --change --owners --herald --force rGTWc84da7041b1199f051d041ca2cc86f3736e0898b
...and you should be good to go. That transcript looks like it didn't try to update the revision this time (just skipping all the work), but ehh whatever.
I don't think there's an easy way: you have to go find the corresponding Differential revision, reopen it, and then probably manually remove the link between the revision and the commit in the database (and I'm not 100% sure that's sufficient). I can't think of an easy way to get back into this code, offhand.